I'm the same, I can't play the sandbox version whatever I do. It seems to be connected to the phone function, which is probably why they can't do anything to permanently correct it. Because the only longterm solution is probably to remove the phone completely, which would mean revamping the whole of Chapter 2. Some people also appear to have compatibility issues with Windows 11, which is caused by a flaw in that. And another Dev has also alerted me, to weaknesses within Renpy itself, which can sometimes cause serious issues with old saves. So there may be factors that are totally beyond the Devs control?
One thing is for sure. There is no easy solution to this issue. If we eventually get a third chapter of this game, perhaps they'll completely remove the phone, and that will solve this issue for a lot of people? But until then, the VN version appears to be the only workable alternative.
As I said, this doesn't affect everybody. Some people can use their old saves on the sandbox version, without getting any exceptions and for many more it's corrected if they restart the game or only use the saves provided by the Devs. But restarting every single update is a pain in the ass, as is not being able to follow the path through the game, that you'd like. That's why I'm currently forced to play the VN version.